What is Blastocyst?

An embryo that has developed for five to seven days after fertilization and has developed 2 distinct cell types and a central cavity filled with fluid (blastocoel cavity) is called a Blastocyst. The cells in a blastocyst have just started to differentiate. The surface cells that surround the cavity (just under the outer shell) are called the trophectoderm and will later develop into the placenta. The more centrally located group of cells are called the inner cell mass and will become the fetus.
In conventional IVF, the embryos are  transferred to the uterus after 48 hours at 4-8 cell stage. In natural conception,  the embryo reaches the uterine cavity only on day FIVE. With the availability of new extended culture medium, we can now culture the embryos in the laboratory till the blastocyst stage (i.e. day 5-6). The blastocyst culture and day 5 embryo transfer procedure facilitates selection of the best quality embryos for transfer to the uterus of the mother. With blastocyst embryo transfer, we can transfer fewer embryos - reducing risks for multiple pregnancy - while keeping overall pregnancy rates high.